1. Field of the Invention
The invention relates generally to graphics rendering and, more specifically, to a system and method for intuitive manipulation of the layering order of graphics objects.
2. Description of the Related Art
In conventional two-dimensional computer graphics, layered modeling produces a target image by painting overlapping layers on a digital canvas or document in the order of decreasing depth. Many applications employ layered modeling techniques to render graphics objects in a digital canvas or document. For example, Microsoft Powerpoint and Adobe Photoshop both employ layers to allow users to create and manipulate graphics objects.
With these applications, a user typically changes the layering order of graphics objects by adjusting the absolute depth of the layer containing the graphics object the user wants to reorder. One approach used for adjusting the absolute depth of layers requires a user to first select a graphics object and then use a menu to change the depth of the layer associated with the graphics object. For example, a user of Powerpoint or other Microsoft Office applications must first select the graphics object and then use a textual list that is part of the right-click menu to change the absolute depth of the layer associated with the selected graphics object. The textual list of commands includes commands that change the absolute depth of the layer by one position, such as Bring Forward and Send Backward, as well as commands that move the layer to the absolute top or bottom of all layers in the document, such as Bring to Front and Send to Back.
Another approach used for adjusting the absolute depth of layers requires a user to change the absolute depth of a layer by dragging a layer up or down in a layer palette tool. For example, Photoshop and the GNU Image Manipulation Program (GIMP) employ a layer palette tool for manipulating the absolute depth of layers in composite images. The layer palette tool displays graphical thumbnails that represent each of the individual layers in the canvas. The user changes the absolute depth of a layer by dragging the thumbnail representing the selected layer above or below the layer immediately adjacent to the selected layer.
One drawback to these approaches is that when two overlapping graphics objects are associated with different layers that have a large disparity in the absolute depth of the digital canvas or document, the user may be required to repeat a command multiple times before the two graphics objects switch relative positions in the layering order. For example, a user may have to select the Bring Forward command five times in order to move a layer up five positions in absolute depth, or a user may have to drag a layer up five positions in the user palette tool to move the layer up five positions in absolute depth. Furthermore, when two non-overlapping graphics objects switch relative position in the layering order, the rendered display of the digital canvas or document remains the same. Therefore, the user may be confused as to whether any layers have actually changed position in the absolute depth in the digital canvas or document.
As the foregoing illustrates, what is needed in the art is an improved approach for manipulating the layering order of graphics objects in a digital canvas or document.